Colin Firth has won the best actor trophy at the Screen Actors Guild awards for his role as King George VI in The King's Speech, which also took a second honour for its overall cast at the ceremony in Los Angeles.

The two prizes capped a week of Hollywood triumph for the monarchy saga, which is building momentum for the Academy Awards on 27 February, for which the Facebook drama The Social Network previously had looked like the favourite.

Natalie Portman earned the best actress award at the SAG ceremony for Black Swan, while The Fighter co-stars Christian Bale and Melissa Leo swept the supporting acting honours, boosting their own prospects come Oscar night.

The King's Speech leads Oscar contenders with 12 nominations, among them best picture and actor for Firth, who has been the awards favourite virtually since the film premiered at festivals six months ago.

"Until today, I would say probably, if ever I felt that I had a trophy which has told me that something's really happening for me, it was my SAG card," said Firth.

"Growing up in England, it's not something you expect to see in your wallet, really," Firth continued. "And so it has this glow, and I used to flash it around, hoping it would get me female attention, entry into nightclubs and top-level government departments. It didn't."

Many winners had gushing words for the protection and fellowship their union offers.

"I've been working since I was 11 years old, and SAG has taken care of me," said Portman, who won for her role in Black Swan as a ballerina losing her grip on reality. "They made sure I wasn't working too long and made sure I got an education while I was working."

Bale is a strong favourite for the supporting actor Oscar as real-life fighter Dicky Eklund, whose career unravelled amid drugs and crime. Eklund briefly joined Bale on stage, the actor telling him he's "a real gentleman".

"I love acting. I love what we do," Bale said. "It's so bloody silly at times, isn't it? It's like playing dress-up, and other times it is so meaningful. I just enjoy that so much we get to walk in other people's shoes. Life without empathy is no fun at all. "

Leo, who plays the domineering matriarch of a boxing family in The Fighter, was speechless for a moment after taking the stage.

"I'm much better when I have my words written for me and somebody's costumes to put on," said Leo, 50 "This has been an extraordinary season for me."

Betty White, who is having her own career resurgence in her 80s, won TV comedy actress for Hot in Cleveland.

"I must say this is the biggest surprise I've ever had in this business. There wasn't a prayer. I am so lucky to be ... at 89, to be working," White said, pausing as the crowd interrupted her with effusive applause. "You didn't applaud when I turned 40."

Alec Baldwin won his fifth straight guild award for best actor in a comedy series for 30 Rock.

"I don't know what to say. This is ridiculous. I'm so happy," Baldwin said. "We've had a great year with the show."

Modern Family won for overall cast performance in a TV comedy.

Steve Buscemi of Boardwalk Empire and Julianna Margulies of The Good Wife won as best actors in a TV drama. Boardwalk Empire, a Prohibition-era gangster series, also won for overall TV drama cast performance.